This invention relates to high power gas transport lasers.
U.S. Pat. No. 3,772,610 describes a relatively compact carbon dioxide laser capable of producing continuous output power of 1 to 2 KW at 10.6 .mu.. This laser has been used successfully for industrial purposes such as cutting, welding and heat treating but is limited as indicated above in its power generating capabilities. There is a continuing need for still higher power industrial lasers of this type while nevertheless retaining the advantages of practicable weight and size.
Higher power is obtained by increasing the magnitude of the discharge current in the flowing gas. One way to increase the discharge current without arcing is to increase the cathode surface area per unit length of the cylindrical cathode by increasing the diameter which in turn causes a larger impedance to the high velocity gas flowing by the cathode. This results in reduction in gas flow velocity which is detrimental to both output power and discharge stability.
The prime disadvantage in use of the single cylindrically tubular cathode to extend the power limits, then, is that its surface area cannot be increased as required to provide higher current without adversely blocking gas flow. If on the other hand the larger cathode surface area is obtained with a streamlined cross-sectional configuration such as an airfoil shape, electrical performance is unsatisfactory because arcs form due to the absence of turbulence in the gas adjacent to the cathode surface.
Another way to provide a larger cathode surface without substantial disruption of gas flow is by utilizing a plurality of cylindrical cathodes as described in the copending application of T. S. Fahlen and R. F. Kirk, Ser. No. 662,941, assigned to the assignee of this invention. While the plural cathode arrangement has been used successfully in attaining greater output power, such a laser is less efficient to operate because of the ballast resistors required for balancing current flow through the cathodes.